1. Field of the Invention
This invention is directed to fabricating a wick system in a heat pipe by the eutectic bonding of a wick screen to the interior of a heat pipe body, and more particularly to the eutectic bonding of a stainless steel screen to the surface of a titanium pipe.
2. Description of the Prior Art
The joining of dissimilar metals is fairly well documented in methods of brazing as by an interlayer of a material which functions as a eutectic alloying agent. An example of this formation of bonding is seen in Galasso et al U.S. Pat. No. 4,034,454 of July 12, 1977. An example of joining titanium and titanium alloys using a brazing material can be found in Hanink U.S. Pat. No. 3,466,737 of Sept. 16, 1969. A further example of joining titanium and steel is found in Japanese Pat. No. 56-71590(A) of June 15, 1981 by Takashi Oomae. Additionally, the patent of Wright U.S. Pat. No. 3,121,949 of Feb. 25, 1964 is directed to a method for manufacturing titanium clad steel.
None of the foregoing examples is concerned with the bonding of stainless steel to titanium by the direct contact of these two materials. The prior art is generally directed to the use of an interlayer of material which functions as a eutectic alloying agent. However, in the fabrication of heat pipes where a wick system on the interior of the heat pipe is an important requirement, the teaching of the foregoing prior art fails to provide the necessary guidance.
The design of heat pipe systems requires the placement of a fine metal screen or wick in fixed position on the interior surface of a metal tube. The screen is normally 200-400 mesh with very small openings which does not lend itself to conventional welding processes as a significant portion of the screen is destroyed. Furthermore, conventional brazing methods are not acceptable because of the uncontrollable capillary action of the brazing alloy which fills the screen openings. When resort to mechanical attachment of the screen to the tube is had, spaces between the screen and the tube wall occur which lowers the wicking efficiency of the heat pipe.